1. Field of the Invention
The present invention relates to a treating agent to impart lubricity and corrosion resistance to the surface of electrical contacts coated with noble metal.
2. Description of the Related Art
Electrical contacts are coated commonly with noble metal (such as gold, palladium, and silver) or alloy thereof. Nowadays, their coating film getting very thin for cost reduction or owing to technical advancement. Especially, gold coating is being replaced by palladium (or palladium alloy) coating with flash gold plating. Reduction in coating thickness poses a problem with corrosion due to pinholes. In addition, electrical contacts with thin gold plating alone needs great force to be pushed in and pulled out, with the possibility of it wearing off. A common way to improve corrosion resistance, lubricity, and wear resistance is by post-treatment for the surface of electrical contacts.
The post-treatment is accomplished by dipping electrical contacts in a solution of a lubricant and corrosion inhibitor in a halogenated organic solvent. The lubricant includes liquid paraffin and wax which remain on the surface of electrical contacts, and the corrosion inhibitor clogs pinholes, thereby contributing to corrosion resistance. Much has been studied about solid and semi-solid lubricants. Antler (Bell Laboratory) cited in his work [Wear, 6, pp. 44-66 (1963) and Connectors Interconnections Symp. Proc. 19th, pp. 1-13 (1986)] typical reports such as Stanford Res. Inst., Rept. No. 12 for Project No. PU-31521, Jul. 1, 1961 (on wax), Proc. Inst. Elec. Engrs. (London) 100 174 (1953) (on Teflon resin), and Pa. State Univ., Jun. 8-12, 1959 (on petroleum jelly). Other common lubricants are liquid paraffin and squalane.
After that, a new high-performance lubricant was developed for spacecraft equipment and nuclear power equipment. It is polyphenyl ether (such as bis(phenoxyphenoxy)benzene and bis-(m-(m-phenoxyphenoxy)phenyl)ether). It was shown by the above-mentioned Antler's work to exhibit good lubricating characteristics when applied to electrical contacts. Since then it has come into general use.
Some sealing lubricants have been proposed as follows:
[1] A solution in trichloroethane of 0.1-3 wt % petrolactam (ointment-like petroleum wax) and 0.05-3 wt % chelate-forming cyclic nitrogen compound(s). JP, A, 4-193982. PA1 [2] A solution in trichloroethane of 0.1-3 wt % paraffin wax and 0.05-3 wt % alkyl-substituted naphthalenesulfonate(s). JP, A 4-193992. PA1 [3] A solution of 0.1-5 wt % paraffin wax and petrolactam(s) in petroleum solvent (such as toluene and xlene), alcoholic solvent (such as isopropyl alcohol), or paraffinic solvent (such as n-decane). JP, A 7-258889.
Commercial sealing lubricants for plated contacts are classified according to metals (such as gold, silver, and tin) to which they are applied. All of them are solutions in 1,1,1-trichloroethane or fluorocarbon solvent. Such solvent solutions, however, are being replaced by aqueous solutions in consideration of their effect on environment. For example, JP, A, 7-258891 discloses treatment with an organic solvent solution of 0.1-5 wt % paraffin wax and petrolactam(s) floating in layer (1-10 mm thick) on an aqueous solution. JP, A, 7-258894 also discloses an aqueous solution of fatty acid soap and aminocarboxylic acid for use as a sealing lubricant.
There are some disclosures concerning polyphenyl ether used for lubrication of tin-plated contacts. For example, JP, B2, 3-80198 discloses a polyphenyl ether-based lubricant containing a copolymer of perfluoroalkylene and acrylate ester or a phosphate ester having benzene rings as lipophilic groups in an amount more than 0.5%. JP, B2, 5-22322 also discloses a tin-plated connector contact treated with a polyphenyl ether-based lubricant containing a phosphate ester surfactant having benzene rings as lipophilic groups in an amount more than 0.5%. The first disclosure is concerned with a method of applying polyphenyl ether directly to the tin plating film or tin-lead alloy plating film on contacts which is poor in wettability. The second disclosure is concerned with a contact treated with polyphenyl ether.